Pulverizing apparatus



Sept. 2 9, 1959 E. M. POOLE PULVERIZING APPARATUS Filed April 22, 1957INVENTOR- Edward M. Poole- ATTORNEY A A 2,906,467 Patented Sept. 29,1959

PULVERIZING APPARATUS Edward M. Poole, Barberton, Ohio, assignor to TheBabcock & Wilcox Company, New York, N.Y., a corporation of New JerseyApplication April 22, 1957, Serial No. 654,229

3 Claims. (Cl. 241-5 3) The present invention relates in general toimprovements in the construction and operation of pulverizers, and moreparticularly to pulverizers of the general type shown in U.S. Patent2,275,595 in which horizontally arranged rolling grinding elements arecircumferentially positioned between and in contact with upper and lowergrinding rings. a

In the pulverization of any material, particularly in air sweptpulverizers wherein the material is pulverized and continuously airswept to remove the finished prodnot, the arrangement of partsmust'besuch as to obtain maximum grinding effect without overgrindingthe material being processed. Many variables enter into the efliciencyof pulverization, where one of the variables relates to the materialbeing ground and its general grinding characteristics. However, on anyparticular material, the efliciency of pulverization is largelyinfluenced by the amount of effective grinding surface available forpulverization. Ordinarily, an increase in the surface area available forgrinding will increase the pulverizing capacity of a unit, providing thepulverized material is removed from the grinding substantially as it isproduced and overgrinding is avoided.

The amount of grinding surface available in any pulverizer is limited,for practical reasons, to the effectiveness of the removal of thefinished product from the grinding zone so as to avoid overgrinding ofthe material. Thus, an efficient pulverizer is largely a compromisebetween the area available for pulverization and an arrangement of partswhereby the finished material may be efiiciently removed from thegrinding zone.

In the present invention, the capacity of a pulverizer is increased withan actual reduction in the grinding area available for pulverization.The results of the reduction of surface area are entirely unexpected inthat while it would be expected the pulverizer capacity of a unit wouldbe reduced by a reduction in grinding surface area,'actual operation hasshown that the capacity has been increased. Actually, while the surfacearea available for pulverization has been decreased, the position of thegrinding surfaces has been slightly altered in relationship to thestructures heretofore in use without adversely affecting the grindingcapacity of the unit.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming apart of this specification, For a better understanding of the invention,"its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated and described a preferred embodimentof the invention.

Of the drawings:

Fig. 1 is a perspective, partly in section, of a pulverizer constructedand arranged according to the present invention; and

Fig. 2 is an enlarged elevation, in section, of a portion of thegrinding surfaces shown in Fig. 1. a a

In general, the pulverizer illustrated includes a cylindrical upperhousing 10 and a lower section 11 supported on a foundation 12. Thelower section encloses the pulverizer gear drive which includes ahorizontal pinion shaft 13 arranged to drive a vertical drive shaftaxially disposed in the section 11 and the housing 10. The drive shaftextends upwardly through supporting bearings (not shown) arranged in abase plate 14 forming the top of the base section 11. The upper housingis detachably secured to the base plate and encloses the grinding partsof the pulverizer which comprises a drive yoke-15 of generallyfrusto-conical form keyed on the upper part of the drive shaft and alower annular grinding ring 16 supported upon'and dowelled to aflattened lower portion of the drive yoke 15. The upper face of thegrinding ring 16 is shaped to form a circular track for a-row of rollinggrinding elements, preferably balls 17 of wear resistant alloy. Thehalls support a non-rotary upper grinding ring 18 having a circular balltrack formed in its lower face. The upper grinding ring is provided withlugs 20 formed adjacent its upper surface at circumferentially spacedpositions where the lugs are each provided with a socket for theinsertion of a coil spring 21. The upper end of the coil spring 21 isinserted in a socket formed in the lower end of'a vertically adjustablesupport element 22. The assembly described is arranged to exert aresilient downward grinding pressure on the grinding parts, and asdisclosed in U.S. Patent 2,595,587, the springs are also utilized torestrain rotational movement of the upper grinding ring 18.

-The material to be pulverized is supplied by a feeder 23. of therotating table type, Where the discharge from the feeder enters throughthe upper portion of the pulverizer housing 10. The raw material fallsthrough the influence of gravity to the inclined surface of the yoke 15,and the yoke rotation distributes the material circumferentially to thegrinding zone formed by the grinding rings 16 and 18 and the circularrow of balls 17. Due to the efiect of centrifugal force, the rawmaterial tends to flow outwardly through the grinding zone and todischarge therefrom at an oblique angle to the periphery of the grindingelements. The angle of discharge of the pulverized material from thegrinding zone depends upon the rotational speed of the lower ring 16.

As shown in Fig. l, the pulverizer is of the air-swept type wherein astream of primary or carrier air passes through the pulverizer from anexternal source such as a blower (not shown). The air is delivered tothe pulverizer at a superatmospheric pressure through the duct 26 to anannular wind box 27.v The primary air is ordinarily preheated to atemperature of from to 600 F., depending upon the moisture content ofthematerial being pulverized. The annular wind box 27 surrounds thelower portion of the pulverizer housing 10 and is' provided with anannular inlet passage 28 through the housing having a plurality ofcircumferen-. tially.spac ed vanes 30 therein, which areinclined so asvto cause a swirling of the air in the same direction as the rotation ofthe lower grinding ring 16.

As shown particularly in Fig. 2, the air entering the pulverizer housingis directed upwardly through a reing ring 16. The throat passageway 31is inclined upwardly. and outwardly so as to direct a high velocitystream of carrier air passing therethrough toward thewall of the housing10. A circumferentially spaced series of plows 34 are attached to theannular stationary mem-' ber of the throat 31 at a position upwardlyspaced from the rotating lower grinding ring 16. As hereinafter de--scribed, the plows are utilized to prevent the accumulation of an airsuspended mass of relatively coarse material adjacent the dischargeopening of the throat 31.

Immediately above the throat 31 and the plows 34, the cross-sectionalarea for flow of air and entrained pulverized material is increased.Thus, the reduced velocity of the carrier air will permit a separationof the coarser particles of pulverized material from the carrier airstream. These coarser particles have a tendency to drop out ofsuspension on the upper grinding ring 18 of the grinding zone. Ashereinafter described, the upper grinding ring 18 is constructed andarranged to facilitate the recirculation of the coarser particles backto the grinding zone. The finer pulverized material, maintained insuspension in the carrier air stream, passes upwardly through the upperportion of the pulverizer housing to enter a classifier 35.

As shown in Fig. 1, and disclosed in US. Patent 2,762,- 573, theclassifier is of the stationary type and consists of an uppercylindrical portion attached to the cover plate 36 of the pulverizer andprovided with a circumferential series of adjustable deflector vanes 37positioned in the wall thereof. Immediately below the cylindricalportion of the classifier is provided an inverted frustoconical portion38 which merges into a lower cylindrical neck 40 which extends below andencircles the upper end of the rotating yoke 15. As disclosed in saidpatent, the upper end portion of the yoke is provided with rejectorvanes 41, which tend to discharge coarse material separated in theclassifier downwardly onto the upper surface of the voke 15 forrecirculation to the grinding zone.

Within the classifier, the fine particles of pulverized material whichremain in suspension in the carrier air stream pass upwardly through acentrally positioned. depending cylindrical baflle 42 and an outlet 43in the cover plates 36 into a two-way distributor 44. The distributor isprovided with a pair of upwardly extending discharge pipes 45 and 46 forthe transportation of the air entrained pulverized material to burnersor other points of use. Each of the bifurcated outlet branches 47 and 48from the pulverizer distributor 44 is provided with a flap valve 50 suchas shown in branch 47 so that one or the other or both of the pipes 45and 46 may be tightly closed.

In accordance with the present invention, the upper grinding ring 18 isprovided with a plurality of ports 51 extending upwardly and outwardlythrough the upper grinding ring 18. As shown particularly in Fig. 2, thegrinding ring 18 is provided with an annular recess 52 opening to thelower grinding surface 53 of the ring where the recess 52 opens to eachof the circumferentially spaced ports 51 so that any recirculated coarsematerials discharging downwardly through the ports may be distributedthroughout the circumference of the grinding zone formed between therings 16 and 18, and the balls 17. The recess 52 is formed in the ring18 for fabrication purposes, so as to permit an economical arrangementfor supporting cores and chill plate in casting the ring. Actually, therecess has no substantial functional effect on the use of the ring inthe grinding zone. The ports 51 are elongated circumferentially of thering and have a radial width substantially equal to the radial width ofthe recess 52. In the illustrated embodiment of the invention, thepulverizer is constructed with a pitch diameter of 70 inches center tocenter of the balls 17. The balls, as originally installed, are 10inches in diameter, and the upper grinding ring 18 has a radial arc ofcontact with the balls of approximately inches while the ports 51 andthe recess 52 have a radial width of 2 /2 inches adjacent the grindingsurface of the ring. In the ring 18 shown, the length of each port 51 isapproximately 8 inches, with a spacing between circumferentiallyadjacent ports of approximately 3 inches. It will be recognized that thedimensions of individual ports will vary with the dimensions of therings, but the radial width dimension should be maintained as near as 2to 2 /2 inches, even in smaller rings, consistent with structuralstrength requirements of the ring.

As shown in Fig. 2, the upper grinding ring 18 is shaped with a lowerannular grinding surface which contacts the upper segment of thecircumferential series of grinding balls 17. The ring 18 is of upwardlyincreasing diameter, and in cross-section the inner surface 54 curvesupwardly and outwardly for a maximum thickness of approximately 9inches. The outer surface 55 inclines upwardly at an angle ofapproximately 70 degrees with respect to the horizontal to join theupper surface 56 of the ring which inclines outwardly and downwardly atan angle of approximately 45 degrees. The circumferential row of ports51 is offset outwardly of the ball centerline about inch and the ports51 are curved outwardly, parallel to the inner surface 54 of the ring,to a flared opening in the top surface 56.

With the construction described, the wear on the contact surfaces of therings 16 and 18, and balls 17 will be substantially vertical and theentire assembly will move downwardly as wear occurs, while maintainingeffective surface contact between the relative moving contact surfacesof the assembly. The outwardly flared section of the ring aids inmaintaining the vertical wear movement of the assembly.

In the operation of the pulverizer described, a material such asbituminous coal is delivered through the pulverizer to the feeder 23.The raw coal discharging upon the upper surface of the yoke 15 will moveoutwardly into the grinding zone formed by the rings and balls, and willbe pulverized by the rolling action of the grinding elements. As thecoal is pulverized, the material passing through the grinding zone isdischarged outwardly into the high velocity stream of carrier airpassing upwardly through the throat 31. The carrier air entrains andlifts the pulverized material and discharges the material toward theinner surface of the pulverizer housing 10. The coarser materialsdischarged upwardly by the air will have a tendency to fall out ofsuspension and to discharge inwardly of the pulverizer into the ports 51formed in the upper grinding ring 18. The coarser materials fallingthrough the ports 51 will be discharged to the ring and ball assemblyand will be distributed to the grinding zone. A major portion of thegrinding effect of the grinding zone on such recirculated coarse coalwill occur between the balls 17 and the surface 53 of the grinding ring18. The remaining portion of the finer pulverized coal will bedischarged into the classifier 35 where a further separation of fine andcoarse material occurs, with the fines being discharged through thepipes 45 and 46, and the coarser material being recirculated to thepulverizing zone. While the total area of contact between the balls 17and the upper grinding ring 18 has been reduced substantially inproportion to the contact area removed in forming the ports 51, ascompared with upper grinding rings heretofore in use, the capacity ofthe unit has actually been increased as much as 5 to 10%.

While the exact reasons for this increase in grinding capacity is notknown, it is believed that the improvement in the operation of the unitresults from an improved separation of coarse material from the massdischarged fromthe grinding zone and the prompt recycling of the majorportion of the coarsest material back to the grinding zone. Thisimmediate separation of the coarsest material from the grinding zone inthe annular space immediately above the pulverizer throat eliminates anytendency to maintain a suspended mass of pulverized material immediatelyabove the throat 31 which would thereby tend to choke the pulverizerdischarge. It has also been observed that the upper grinding ringconstructed in accordance with the present invention has increased theservice life of the ring as compared with the rings of the same materialheretofore in use. This again is probably due to the freedom forrecirculation of the coarse material to the grinding zone so that anytendency to choke the grinding zone is substantially eliminated undernormal conditions of air 110w and fuel flow to the unit.

While in accordance with the provisions of the statutes I haveillustrated and described herein the best form and mode of operation ofthe invention now known to me, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by my claims, andthat certain features of my invention may sometimes be used to advantagewithout a corresponding use of other features.

The claims are:

1. A pulverizer comprising a housing, a plurality of rolling grindingelements arranged for rotational movement in a horizontal circular pathbetween the grinding surfaces of upper and lower opposed grinding rings,the radial external dimension of said upper ring being less than saidlower ring to define an increased area between the periphery of saidupper ring and said housing, means for rotating one of said rings aboutthe axis of said circular path, means for passing an annular stream ofcarrier fluid upwardly past the outer periphery of said rings to entrainpulverized material discharging from said grinding elements, theincreased area adjacent the periphery of said upper grinding ringreducing the velocity of carrier medium flow past said upper ring tode-entrain coarser pulverized materials therefrom, the upper grindingring having a lower surface of contact bearing substantially on the apexof said rolling grinding elements, and means defining a plurality ofcircumferentially spaced ports extending through said upper ring andopening to the grinding surface thereof for downward and inward movementof said de-entrained material through said ports.

2. A pulverizer comprising a housing, a plurality of rolling grindingelements arranged for rotational movement in a horizontal circular pathbetweenthe grinding surfaces of upper and lower opposed grinding rings,the radial external dimension of said upper ring being less than saidlower ring to define an increased area between the periphery of saidupper ring and said housing, means for rotating the lower of said ringsabout the axis of said circular path, means for passing an annularstream of carrier fluid upwardly past the outer periphery of said ringsto entrain pulverized material discharging from said grinding elements,the increased area adjacent the periphery of said upper grinding ringreducing the velocity of carrier medium flow past said upper ring todeentrain coarser pulverized materials therefrom, the upper grindingring having a lower surface of contact bearing on an upper segment ofsaid rolling grinding elements, and means defining a plurality ofcircumferentially spaced ports extending through said upper ring andopening to the grinding surface thereof for downward and inward movementof said de-entrained material through said ports.

3. A pulverizer comprising a housing, a plurality of rolling grindingelements arranged for rotational move.- ment in a horizontal circularpath between the grinding surfaces of upper and lower opposed grindingrings, the radial external dimension of said upper ring being less thansaid lower ring to define an increased area between the periphery ofsaid upper ring and said housing, means for rotating the lower of saidrings about the axis of said circular path, means for passing an annularstream of carrier fluid upwardly past the outer periphery of said ringsto entrain pulverized material discharging from said grinding elements,the increased area adjacent the periphery of said upper grinding ringreducing the velocity of carrier medium flow past said upper ring tode-entrain coarser pulverized materials therefrom, the upper grindingring having a lower surface of contact bearing substantially on theupper apex of said rolling grinding elements and having an upwardly andoutwardly flaring cross-sectional configuration with an upwardly andinwardly inclined upper outer surface, and means defining a plurality ofcircumferentially spaced ports extending through said upper ring ringfrom said inclined upper outer surface and opening to the grindingsurface thereof for downward and inward movement of said de-entrainedmaterial through said ports.

References Cited in the file of this patent UNITED STATES PATENTS935,161 Nix Sept. 28, 1909 2,092,310 Hardgrove Sept. 7, 1937 2,762,573Culp Sept. 11, 1956 FOREIGN PATENTS 573,163 Germany Mar. 23, 1933573,582 Germany Apr. 4, 1933

